To understand the role the transverse-tubules play in the process of excitation-contraction (E-C) coupling in muscle it is essential to obtain a better knowledge of the structure and function of components of these membranes. In order to attain this goal we will prepare purified transverse-tubule membranes from cardiac and skeletal muscles. Monoclonal antibodies obtained against these membranes will be used as probes to identify and isolate the molecular components of these membranes associated with specific function. Among these components we hope to identify the macromolecules involved in E-C coupling by using the antibodies on single fibre preparations and on a triad-containing microsomal fraction capable of accumulating and releasing calcium under physiological conditions. Structural and electrophysiological evidence indicates that different mechanisms of excitation-contraction coupling might operate in cardiac and skeletal muscles. Antibodies will be used in comparative studies to answer questions concerning the relation of morphological and antigenic differences between T-tubules from cardiac and skeletal muscles to their functional properties. The antibodies will also be used for electron microscopic localization of the membranes constituents in situ. By carrying out the proposed studies in parallel for both cardiac and skeletal muscle, we hope that differences as well as similarities between the two systems can be exploited to gain an insight into the molecular organization of each system.